Some Basic Principles of Developmental Robotics Alexander Stoytchev, Member, IEEE
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IEEE TRANSACTIONS ON AUTONOMOUS MENTAL DEVELOPMENT, VOL. 1, NO. 2, AUGUST 2009 1 Some Basic Principles of Developmental Robotics Alexander Stoytchev, Member, IEEE Abstract—This paper formulates five basic principles of devel- ioms of the field. There are some recurring themes in the devel- opmental robotics. These principles are formulated based on some opmental learning literature and in the author’s own research, of the recurring themes in the developmental learning literature however, that can be used to formulate some basic principles. and in the author’s own research. The five principles follow logi- cally from the verification principle (postulated by Richard Sutton) These principles are neither laws (as they cannot be proved at which is assumed to be self-evident. This paper also gives an ex- this point) nor axioms (as it would be hard to argue at this point ample of how these principles can be applied to the problem of au- that they are self-evident and/or form a consistent set). Never- tonomous tool use in robots. theless, they can be used to guide future research until they are Index Terms— Artificial intelligence, developmental robotics, in- found to be inadequate and it is time to modify or reject them. telligent robots, learning systems, principles, psychology, robots, Five basic principles are described below. robot programming. II. THE VERIFICATION PRINCIPLE I. INTRODUCTION Developmental robotics emerged as a field partly as a reac- tion to the inability of traditional robot architectures to scale up EVELOPMENTAL robotics is one of the newest to tasks that require close to human levels of intelligence. One of D branches of robotics [1]–[3]. The basic research as- the primary reasons for scalability problems is that the amount sumption of this field is that “true intelligence in natural and of programming and knowledge engineering that the robot de- (possibly) artificial systems presupposes three crucial proper- signers have to perform grows very rapidly with the complexity ties: embodiment of the system, situatedness in a physical or of the robot’s tasks. There is mounting evidence that pre-pro- social environment, and a prolonged epigenetic developmental gramming cannot be the solution to the scalability problem. The process through which increasingly more complex cognitive environments in which the robots are expected to operate are structures emerge in the system as a result of interactions with simply too complex and unpredictable. It is naive to think that the physical or social environment” [2]. this complexity can be captured in code before the robot is al- Many fields of science are organized around a small set of lowed to experience the world through its own sensors and ef- fundamental laws (e.g., Newton’s laws in Physics or the fun- fectors. damental laws of Thermodynamics). Progress in a field without For example, consider the task of programming a household any fundamental laws tends to be slow and incoherent. Once the robot with the ability to handle all possible objects that it can fundamental laws are formulated, however, the field can thrive encounter inside a home. It is simply not possible for any robot by building upon them. This progress continues until the laws designer to predict the number of objects that the robot may are found to be too insufficient to explain the latest experimental encounter and the contexts in which they can be used over the evidence. At that point the old laws must be rejected and new robot’s projected service time. laws must be formulated so the scientific progress can continue. There is yet another fundamental problem that pre-program- In some fields of science, however, it is not possible to formu- ming not only cannot address, but actually makes worse. The late fundamental laws because it would be impossible to prove problem is that programmers introduce too many hidden as- them, empirically or otherwise. Nevertheless, it is still possible sumptions in the robot’s code. If the assumptions fail, and they to get around this obstacle by formulating a set of basic prin- almost always do, the robot begins to act strangely and the pro- ciples that are stated in the form of postulates or axioms, i.e., grammers are sent back to the drawing board to try and fix what is wrong. The robot has no way of testing and verifying these statements that are presented without proof because they are considered to be self-evident. The most famous example of this hidden assumptions because they are not made explicit. There- approach, of course, is Euclid’s formulation of the fundamental fore, the robot is not capable of autonomously adapting to situa- axioms of Geometry. tions that violate these assumptions. The only way to overcome this problem is to put the robot in charge of testing and verifying Developmental robotics is still in its infancy and it would be premature to try to come up with the fundamental laws or ax- everything that it learns. To make this point more clear consider the following ex- ample. Ever since the first autonomous mobile robots were de- Manuscript received February 14, 2009; revised July 27, 2009. First published veloped [4], [5] robots have been avoiding obstacles. After al- date August 11, 2009; current version published October 23, 2009. A prelimi- nary version of this paper appeared in the NIPS 2006 Workshop on Grounding most 30 years of mobile robotics research, however, there is still Perception, Knowledge, and Cognition in Sensori-Motor Experience. not a single robot today that really “understands” what an ob- The author is with the Developmental Robotics Laboratory, Department of stacle is and why it should be avoided. The predominant ap- Electrical and Computer Engineering, Iowa State University, Ames, IA 50011 USA (e-mail: [email protected]). proach in robotics is still to ignore this question entirely and to Digital Object Identifier 10.1109/TAMD.2009.2029989 make the hidden assumption that an obstacle is equivalent to a 1943-0604/$26.00 © 2009 IEEE 2 IEEE TRANSACTIONS ON AUTONOMOUS MENTAL DEVELOPMENT, VOL. 1, NO. 2, AUGUST 2009 short reading on one of the proximity sensors (e.g., laser range this statement in the “weak” sense as he is physically capable finder, sonar, etc.). The problem with this assumption is that it is of performing the verification procedure if necessary. However, true only in some specific situations and not true in general. As the same blind person will not be able to verify, neither in the a result, outdoor robots cannot distinguish grass from steel rods “strong” nor in the “weak” sense, the statement “this object is using a laser range finder. A better approach would be for the red” as he does not have the ability to see and thus to perceive robot to try to drive over the detected object at low speed and see colors. In Ayer’s own words: if it is displaceable and, thus, traversable. Some recent studies “But there remain a number of significant propositions, have used this approach successfully for robot navigation [6]. concerning matters of fact, which we could not verify even After this introduction, the first basic principle can be stated. if we chose; simply because we lack the practical means It is the so-called verification principle that was first postulated of placing ourselves in the situation where the relevant ob- by Richard Sutton in a series of on-line essays in 2001 [7], [8]. servations could be made” [9, p. 36]. The principle is stated as follows: The verification principle is easy to state. However, once a The Verification Principle: An AI system can create commitment is made to follow this principle the implications and maintain knowledge only to the extent that it can verify are far-reaching. In fact, the principle is so different from the that knowledge itself [8]. practices of traditional autonomous robotics that it changes al- According to Sutton, “the key to a successful AI is that it can most everything. In particular, it forces the programmer to re- tell for itself whether or not it is working correctly”[8]. The only think the ways in which learnable quantities are encoded in the reasonable way to achieve this goal is to put the AI system in robot architecture as anything that is potentially learnable must charge of its own learning using the verification principle. In also be autonomously verifiable. other words, all AI systems and AI learning algorithms should The verification principle is so profound that the remaining follow the motto: No verification, no learning. If verification is four principles can be considered as its corollaries. As the con- not possible for some concept then the AI system should not be nection may not be intuitively obvious, however, they will be handcoded with that concept. stated as principles. Sutton also points out that the verification principle eventu- ally will be adopted by many AI practitioners because it of- III. THE PRINCIPLE OF EMBODIMENT fers fundamental practical advantages over alternative methods when it comes to scalability. Another way of saying the same An important implication of the verification principle is that thing is: “Never program anything bigger than your head”[8]. the robot must have the ability to verify everything that it learns. Thus, the verification principle stands for autonomous testing Because verification cannot be performed in the absence of ac- and verification performed by the robot and for the robot. As tions the robot must have some means of affecting the world, explained above, it would be unrealistic to expect the robot pro- i.e., it must have a body. grammers to fix their robots every time the robots encounter a The principle of embodiment has been defended many times problem due to a hidden assumption.